Pile for use in offshore areas having a shifting layer of mud

ABSTRACT

A pile for use in offshore areas having a shifting layer of mud overlaying a competent bottom. The pile is adapted to be driven through the mud and into the underlying bottom so that its lower end is fixedly imbedded in the competent bottom with the pile extending upwardly through the mud. The pile is provided with means for ejecting fluid at a plurality of locations from the interior of the pile into the mud surrounding the pile. The ejected fluid increases the fluid saturation of the mud adjacent to the pile and thereby reduces the forces exerted on the pile by the shifting mud.

United States Patent Maly et al. Dec. 9, 1975 [5 PILE FOR USE IN OFFSHORE AREAS 1,185,582 5/1916 Bignell 61/5374 HAV A SHIFTING LAYER 0F MUD 1,529,112 3/1925 Burns 61/53.74 3,289,421 12/1966 Hindman 61/53.74 Inventors: George Maly, Newport Beach, 3,842,608 10/1974 Turzillo 61/53.74 x

Calif.; Clifton A. Tannahill, Houston Primary ExaminerDennis L. Taylor 73 Assignee; Union on Company of California Attorney, Agent, or FirmRichard C. Hartman; Dean Brea, Calif Sandford; Bernard R. Gans [22] Filed: Aug. 22, 1974 [57] ABSTRACT PP N04 4991650 A pile for use in offshore areas having a shifting layer of mud overlaying a competent bottom. The pile is 52 US. Cl 61/53; 61/53.74 adapted to be driven through the mud and into the 51 Int. c1. E02D 5/22 detlyhlg bottom so that its lower end is fixedly imhed- 58 Field of Search 61/53.74, 53.5, 53, 54, tied in the Competent bottom with the P extending 61/56 175/171 22, 23 upwardly through the mud. The pile is provided with means for ejecting fluid at a plurality of locations from 5 References Cited the interior of the pile into the mud surrounding the pile. The ejected fluid increases the fluid saturation of UNYTED STATES PATENTS the mud adjacent to the pile and thereby reduces the i forces exerted on the pile by the shifting mud. 1,173,355 2/1916 Jones 6l/53.74 7 Claims, 6 Drawing Figures US. Patet Dec. 9 1975 Sheet 1 of2 3,924,14

UH atsnt Dec. 9 1975 Sheet 2 of2 3,924, 1

PILE FOR USE IN OFFSHORE AREAS HAVING A SHIFTING LAYER OF MUD BACKGROUND OF THE INVENTION This invention relates to piles used in offshore areas, and more particularly to piles for use in areas having mud layers susceptible to movement.

In some parts of the world conditions exist which cause great masses of mud to be deposited on the ocean floor. Principally, these deposits are the result of silt, organic matter and other earthen material being deposited at the mouths of large rivers, such as the Mississippi River. Due to the slope of the ocean floor and the continual deposition of new mud, these large masses of mud are unstable, resulting in a continual flow of mud or intermittent mud slides triggered by storms or other disturbances.

In some areas of the Gulf Coast of the United States, where large oit and gas deposits exist, the mud may be as much as 200 feet thick. These petroleum reservoirs are conventionally developed from fixed drilling and production platforms supported upon piles extending through the incompetent mud and imbedded into the underlying competent bottom. The movement of this rnud results in large forces being exerted on these piles; and, in fact, pile-supported structures in the Mississippi River Delta have toppled, apparently as a result of the mud slides.

Thus, while a need exists for a means for reducing the forces exerted on a pile by the movement of mud along the ocean floor, no means or apparatus for reducing these forces has heretofore been proposed.

Accordingly, a principal object of this invention is to provide a pile for use in offshore areas having a layer of mud that is susceptible to movement overlaying a competent bottom.

Another object of this invention is to provide a pile for use in offshore areas that is not detrimentally affected by the movement of mud past the pile.

Yet another object of this invention is to provide a method for reducing the forces exerted by mud moving against a pile extending through the mud and imbedded in the underlying competent bottom.

A further object of this invention is to provide a method for increasing the fluid saturation of the mud adjacent to a pile extending through the mud and imbedded in the underlying competent bottom.

Other objects and advantages will become apparent from the following description.

SUMMARY OF THE INVENTION Briefly, this invention relates to an improved pile for use in offshore areas where the competent ocean bottom is overlain by mud susceptible to or actually in movement, and to a method for reducing the forces that moving mud can exert on the pile. The improved pile is a tubular member provided with apertures strategically located so that they will be within the mud zone when the pile is imbedded in the competent ocean bottom so as to extend upwardly through the mud, and means to supply pressurized fluid to the apertures.

The method of this invention involves ejecting pressurized fluid into the mud surrounding the pile from a plurality of locations spaced around the periphery of the pile within the mud zone. The ejected fluid will increase the fluid saturation of the mud, i.e., fluidized the mud, thereby increasing the lubricity of the mud and 2 reducing the abrasiveness, cohesiveness and shear stress of the mud adjacent to the pile, with a resulting reduction in the forces that the moving mud can exert against the pile.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be more readily understood by reference to the accompanying drawings, wherein like parts are identified by like numerals throughout, and in which:

FIG. 1 is a vertical cross-sectional view of a water body having a shifting layer of mud overlaying a competent bottom and schematically illustrates the installation of a conventional pile in this environment;

FIG. 2 is a horizontal cross-sectional view taken along the line 22 of FIG. 1 schematically illustrating the movement of mud against and around the pile;

FIG. 3 is a vertical cross-sectional view of a'water body having a shifting layer of mud overlaying a competent bottom and schematically illustrates the installation of the improved pile of this invention;

FIG. 4 is a vertical cross-sectional view of one embodiment of the improved pile of this invention installed in a water body having a shifting layer of mud overlaying a competent bottom;

FIG. 5 is a vertical cross-sectional view illustrating another embodiment of the improved pile employing an internally disposed, separate fluid supply conduit; and

FIG. 6 is a vertical cross-sectional view illustrating still another embodiment of the improved pile employing an annular fluid supply conduit.

DETAILED DESCRIPTION FIG. 1 illustrates the installation of a conventional tubular pile in an offshore area covered by water body 8 having shifting layer of mud 6 overlaying competent bottom 4. Tubular pile 2 is driven through mud 6 and firmly imbedded in competent bottom 4. Although pile 2 is shown extending above the surface of water body 8, it need not do so; and, optionally, pile 2 can terminate below the surface of the water.

The mud is more dense than water and therefore settles in a dense layer at the bottom of the water body. The mud layer is incompetent in that it shifts or moves either continuously or intermittently in response to disturbances, such as created by storms, currents, tidal flows, passing ships, detonations, and the like. FIG. 2 illustrates the flow of mud 6 along the path indicated by the arrow so that is impinges against and flows around pile 2. While in some areas the mud will move along generally similar paths, in other areas the magnitude and direction of the muds movement can vary. Because of the thickness of the mud layer, which can be 200 feet or more, and the large areal extent of the mud layer, large masses of mud are involved. Since the mud is abrasive and, because of its low lubricity exhibits a high shear stress, extremely high forces can be exerted against the pile by the moving mass of mud, which requires that the pile -be designed and constructed to withstand the forces exerted against it, thus increasing the cost of such piles. Worse yet, even with these' precautions, pile-supported sturctures in mud slide areas have been known to fail.

The installation of an improved pile in accordance with this invention in an offshore area having a shifting layer of mud overlaying a competent bottom is illustrated in FIG. 3. As in the case of the conventional installation, pile is driven through mud layer 6 and imbedded in underlying competent bottom 4 so as to extend upwardly through the mud layer. Pile 10 can terminate either above or below the surface of water body 8. Fluid at an elevated pressure is ejected from the exterior surface of the pile within the mud zone so as to fluidize the mud in zone 6' immediately surrounding pile 10 to thereby reduce the density, abrasiveness, cohesiveness, and shear stress of the mud contacting the pile and substantially reduce the forces exerted on the pile by the shifting mass of mud. The improved pile employing the fluid ejection technique of this invention is subjected to substantially reduced forces; and thus, is much less subject to structural failure or toppling than a conventional pile under similar conditions.

FIG. 4 illustrates one preferred embodiment of the improved pile of this invention. Pile 10 is comprised of elongated tubular member 12 having tip 14 to facilitate its being driven through mud 6 and into underlying competent bottom 4. Pile 10 can alternatively be openended, with an internal baffle plate located below apertures 16 and so positioned that is would be located above the competent bottom when the pile is permanently imbedded. Vents would also be provided through the pile below the internal baffle plate so as to allow the escape of water and mud from within the pile as the pile is driven into the competent bottom. A plurality of apertures 16 in the wall of tubular member 12 communicating the interior of the tubular member with the exterior thereof are strategically located in that portion of the tubular member that will ultimately be within the mud zone when the pile is installed in an offshore area. Apertures 16 can be simple holes of any geometric configuration, such as circular holes. Also, the apertures through which the fluid is ejected can be provided with jet nozzles 17, as illustrated in FIG. 4. A preferred embodiment utilizes a jet nozzle mounted in a freely rotating ball socket, which produces greater turbulence, mud dispersion, .and reduces clogging of the apertures.

In this embodiment of the invention, the upper end of tubular member 12 is fluid-tightly sealed by means of a cover plate 18, which defines an interior 19 that is utilized to conduct pressurized fluid from fluid inlet 22 to apertures 16 for ejection into the mud zone. Fluid from pressurized fluid source 20 is introduced into interior 19 or tubular member 12 through fluid inlet connection 22, the fluid flowing downwardly through the interior of the tubular member and being ejected through apertures 16, which may be provided with jet nozzles 17, into the mud surrounding the pile to fluidize the mud in zone 6.

Another embodiment of the improved pile having a seperate internal conduit and internal chamber is shown in FIG. 5. Tubular member 12 is provided with smaller diameter tubular conduit 30 extending from fluid inlet connection 22 to chamber 32 formed by the wall of tubular member 12 and transverse bulkhead 34. Fluid from pressurized fluid source 20 is introduced at an elevated pressure through fluid inlet connection 22 and conducted downwardly through internal conduit 30 to chamber 32. The fluid introduced into chamber 32 is discharged through the plurality of apertures 16 in communication therewith to fluidize the mud in zone 6'.

FIG. 6 illustrates another embodiment of the improved pile having an internal annular conduit to conduct the pressurized fluid within the pile. Tubular member 12 is provided with a coaxially mounted, smaller diameter tubular member 40 extending from fluid inlet connection 22 to a point below the apertures 16, where a ringlike bulkhead 42 is provided, in conjunction with cover plate 18, to fluid-tightly seal the space between conduit 40 and tubular member 12 to form the internal annular conduit 44, which also functions as a chamber to supply the apertures with the fluid. Fluid introduced through fluid inlet connection 22 flows downwardly through internal annular conduit 44 and is discharged through apertures 16.

Since the direction of the mud movement cannot always be predicted, or known, it is preferred that the apertures 16 be distributed about the periphery of the pile; and it is even more preferred that the apertures be uniformly distributed about the periphery. The apertures 16 are located in an intermedicate section of the pile that will be within the mud zone when 'the pile is installed in an offshore location. Thus, the longitudinal location of the apertures will depend upon the length of the pile, the expected depth of the mud layer, and the depth to which the pile will penetrate the underlying competent bottom.

Although the apertures can be uniformly distributed along an intermediate section of the pile within the mud layer, or distributed in some other convenient non-uniform arrangement, because the higher hydrostatic pressures at the greater depths result in larger forces being exerted against the pile, it is preferred to eject a larger proportion of the fluid into the lower portion of the mud layer. Thus, it is preferred that the apertures be sized to effect the ejection of a major portion of the fluid into the lower portion of the mud layer and to simultaneously eject a minor portion of the fluid into the upper portion of the mud layer; or alternatively, to employ a larger number of apertures within the lower portion of the mud layer to acheive the same effect.

A preferred system employs a plurality of apertures located in sets of four disposed uniformly about the periphery of the pile at each elevation. Each of the apertures would be spaced apart about the periphery of the pile. The apertures at each successive elevation can be offset about the periphery, e.g., the apertures at each elevation can be offset 45 from those at the adjacent elevations.

Exemplary of one preferred arrangement of apertures employed in the improved piles of this invention is an arrangement in which the apertures in the bottom one-third of the section of the pile within the mud zone are spaced about three feet apart along the length of the pile, the apertures in the middle one-third of the section within the mud zone are spaced about four feet apart, and the apertures in the top one-third of the section within the mud zone are spaced about six feet apart. Four apertures located 90 apart are provided at each level, with the apertures at adjacent levels being offset 45. The apertures are arranged so that the fluid is ejected horizontally away from the pile so as to produce maximum penetration of the fluid into the mud.

Although any of a wide variety of fluids can be employed to fluidize the mud adjacent to the pile, water and air are preferred because of their availability and low cost. The water can be obtained from the water body, with sea water being employed where the platform is installed in an offshore marine area. Under some conditions admixtures of sea water and air are preferred.

The fluid must be ejected through apertures 16 at a pressure sufficient to overcome the existing hydrostatic and hydrodynamic pressures at the aperture locations, and thus penetrate and fluidize the mud. The volumetric ejection rate of the fluid must be sufficient to increase the fluid saturation of the mud so as to create a blanket of fluidized mud around the pile; and if the volumetric ejection rate is high enough, the ejected fluid will create a substantially mud-free blanket of fluid around the pile.

Various embodiments and modifications of this invention have been described in the foregoing description, and further modifications will be apparent to those skilled in the art. Such modifications are included within the scope of this invention as defined by the following claims.

Having now described the invention, we claim:

1. A pile for use in offshore areas having a layer of mud susceptible to movement overlaying a competent bottom, which comprises:

an elongated tubular member driven through a mud layer susceptible to movement and imbedded in the underlying competent bottom so as to extend upwardly through said mud layer; and

fluid ejection means for ejecting fluid outwardly from the interior of said tubular member at a plurality of locations all of which are above said competent bottom and substantially within said mud layer; and for fluidizing the mud adjacent to the pile 2. The apparatus defined in claim 1 wherein said fluid ejection means includes an internal chamber within said tubular member, a plurality of apertures through the wall of said tubular member all of which are located above said competent bottom and substantially within said mud layer, said apertures communicating said internal chamber with the exterior of said member, and fluid supply means for supplying fluid at an elevated pressure to said internal chamber.

3. The apparatus defined in claim 2 including jet nozzles mounted in said apertures.

4. A pile for use in offshore areas having a layer of mud susceptible to movement overlaying a competent bottom, which comprises:

an elongated tubular member driven through a mud layer susceptible to movement and imbedded in the underlying competent bottom so as to extend upwardly through said mud layer, said member having a plurality of apertures through the wall thereof communicating the interior of said member with the exterior thereof for ejecting fluid outwardly from the interior of said tubular member, all of said apertures being located above said competent bottom and substantially within said mud layer fluid inlet means at the upper end of said tubular member for introducing fluid at an elevated pressure into the interior of said tubular member; and fluid source means in fluid communication with said fluid inlet means for supplying said fluid at an elevated pressure to said fluid inlet means; so that fluid introduced into the interior of said tubular member flows downwardly through said member and is ejected through said apertures to fluidize the mud adjacent to the pile.

5. The apparatus defined in claim 4 including an internal chamber in the interior of said tubular member adjacent to said apertures and in fluid communication therewith, and conduit means communicating said fluid inlet means and said internal chamber for conducting said fluid to said internal chamber.

6. The apparatus defined in claim 5 wherein said conduit means includes a smaller diameter tubular conduit coaxially mounted within said tubular member.

7. The apparatus defined in claim 4 including an internal annular conduit defined by said tubular member and a second smaller diameter tubular member coaxially mounted within said tubular member, said internal annular conduit being in fluid communication with said fluid inlet means and with said apertures. 

1. A pile for use in offshore areas having a layer of mud susceptible to movement overlaying a competent bottom, which comprises: an elongated tubular member driven through a mud layer susceptiBle to movement and imbedded in the underlying competent bottom so as to extend upwardly through said mud layer; and fluid ejection means for ejecting fluid outwardly from the interior of said tubular member at a plurality of locations all of which are above said competent bottom and substantially within said mud layer; and for fluidizing the mud adjacent to the pile
 2. The apparatus defined in claim 1 wherein said fluid ejection means includes an internal chamber within said tubular member, a plurality of apertures through the wall of said tubular member all of which are located above said competent bottom and substantially within said mud layer, said apertures communicating said internal chamber with the exterior of said member, and fluid supply means for supplying fluid at an elevated pressure to said internal chamber.
 3. The apparatus defined in claim 2 including jet nozzles mounted in said apertures.
 4. A pile for use in offshore areas having a layer of mud susceptible to movement overlaying a competent bottom, which comprises: an elongated tubular member driven through a mud layer susceptible to movement and imbedded in the underlying competent bottom so as to extend upwardly through said mud layer, said member having a plurality of apertures through the wall thereof communicating the interior of said member with the exterior thereof for ejecting fluid outwardly from the interior of said tubular member, all of said apertures being located above said competent bottom and substantially within said mud layer fluid inlet means at the upper end of said tubular member for introducing fluid at an elevated pressure into the interior of said tubular member; and fluid source means in fluid communication with said fluid inlet means for supplying said fluid at an elevated pressure to said fluid inlet means; so that fluid introduced into the interior of said tubular member flows downwardly through said member and is ejected through said apertures to fluidize the mud adjacent to the pile.
 5. The apparatus defined in claim 4 including an internal chamber in the interior of said tubular member adjacent to said apertures and in fluid communication therewith, and conduit means communicating said fluid inlet means and said internal chamber for conducting said fluid to said internal chamber.
 6. The apparatus defined in claim 5 wherein said conduit means includes a smaller diameter tubular conduit coaxially mounted within said tubular member.
 7. The apparatus defined in claim 4 including an internal annular conduit defined by said tubular member and a second smaller diameter tubular member coaxially mounted within said tubular member, said internal annular conduit being in fluid communication with said fluid inlet means and with said apertures. 